Currently, the conduct of the flight of an aircraft involves different automatic operations that involve many systems. Although the current flight conduct systems have participated considerably in decreasing the accident rate, the fact nevertheless remains that they are placed incrementally by successively adding functions and equipment. This superposition of systems is the historical result of the evolution of technologies in recent decades.
It is thus very common today to arrange equipment on board an aircraft:                a flight management system (FMS): it develops trajectory setpoints to produce a flight plan;        an automatic pilot, also called auto flight control system (AFCS): it performs the guiding function, and to that end is suitable for controlling the setpoints provided by the flight management system (FMS). The use of the FMS combined with the use of the automatic pilot corresponds to the maximum level of automation. The automatic pilot also makes it possible to control the trajectory through the acquisition of parameters set by the crew and by holding these parameters;        an auto-throttle (AT): on fixed-wing aircraft, it is responsible for managing the thrust; and        a flight control system (FCS): it is responsible for the short-term stabilization of the aircraft, and also allows control of the setpoints from the auto flight control system (AFCS).        
This equipment is designed as independent systems having their own interfacing means, i.e., a specific interface for the flight management system, also called multifunctional control display unit (MCDU), a dedicated control station for the auto flight control system, generally made up of rotary controls and buttons, also called flight guidance control panel (FGCP), a control stick or mini stick for the flight control system (FCS), one or several throttles or levers for managing the power of one or several engines.
The complexity caused by this plurality of systems currently plays a non-negligible role in the workload of the crew. In order to be able to perform a commercial flight, the crew must then master several complex and dynamic systems, often operating at different levels of automation.
This multiplicity of systems results in increased costs, both in terms of design and training for the crews that must use them.
Furthermore, this plurality of systems and interfaces may prove to be a source of confusion for the crew. At the origin of incidents/accidents such as loss of control of the aircraft, there is often an incorrect identification of the situation by the crew, or even confusion regarding the system statuses.